Hello, thank you for reaching out to Microsoft Q&A.
What is the exact error message you see when you try to sign in to Minecraft with your Microsoft account (using the new primary alias)?
If you have a Microsoft account, for example, account A, and you add an alias to that same account, you can use either the primary alias or the additional alias to sign in to all Microsoft services and games. However, if you remove the original alias A and set a new alias as the primary one, you will no longer be able to use the old alias to sign in.
Since your question doesn’t include all the details, please provide the following information:
- What is the exact error message you receive when you sign in with your new alias?
- When you go to the Manage how you sign in to your account page, which email address is listed as your primary alias?
- If the issue is only with your password, have you tried resetting your password?